| Description |
Intrinsic factors like nutrients and plant toxins are well known to influence the feeding behavior of mammalian herbivores. However, far less is known about the impact of extrinsic factors such as ambient temperature on herbivore diet selection. Growing evidence suggests that plant secondary compounds become more toxic at higher temperatures due to decreased liver function. This phenomenon, known as temperature-dependent toxicity (TDT), could have critical implications for mammalian herbivores that must balance homeothermy with xenobiotic metabolism in a warming environment. Very little study of TDT has been done in natural systems. For my dissertation, I investigated TDT in a small herbivorous rodent, the desert woodrat (Neotoma lepida). In the Mojave Desert, this species feeds on creosote bush (Larrea tridentata), which produces numerous toxic plant secondary compounds. I explored aspects of TDT with a multilevel investigation using physiological assays, molecular analyses, and behavioral observations. First, I determined that warmer ambient temperatures reduced overall liver function in desert woodrats. Second, I investigated a potential underlying mechanism of TDT by studying the impact of temperature and plant toxins on differential gene expression in the liver of desert woodrats. More genes were up-regulated at cooler temperatures, suggesting that lower temperatures offer a release state, permitting induction of numerous genes in the liver. To explore the impacts of TDT on woodrats, I next tested how temperature affected tolerance to ecologically relevant plant toxins (i.e., creosote resin). Increased temperatures limited the ingestion of creosote resin in desert woodrats and reduced their ability to maintain body mass on a controlled dose of creosote resin. Finally, I examined whether woodrats could behaviorally mitigate the negative effects of TDT by utilizing cooler microclimates. Woodrats not only used cooler microclimates when provided access, but also displayed less body mass loss compared to woodrats without microclimate access. The interactions of ambient temperature and plant toxins present a novel dimension to investigations on herbivore foraging, and further study of TDT will advance the field of plant-animal interactions. Together, my work has expanded our understanding of the challenges that mammalian herbivores may face as global temperatures rise. |
